1. Field of the Invention
The present invention relates to structural improvements on cut-off valves and means for detecting whether fuel tanks are filled up with fuels, cut-off valves and means which are disposed on automobile fuel tanks.
2. Description of the Related Art
In the vicinity of automobile fuel tanks, a vaporized-fuel circulating system, a so-called evaporator circuit, is disposed. The evaporator circuit leads vaporized fuels from fuel tanks to external canisters. The vaporized fuels are then adsorbed to activated carbon and the like, and are stored temporarily therein. Thus, the evaporator circuit inhibits the pressure increment within fuel tanks, pressure increment which results from the increment of vapor pressure. The canisters are connected with engines, and engines exert an inlet negative pressure to release the adsorbed vaporized fuels from activated carbon to mix them into an air-fuel mixture. Accordingly, the adsorbed vaporized fuels are used again as fuels.
The evaporator circuit is naturally provided with an opening, a so-called evaporator opening, which is formed in fuel tanks. The evaporator opening is generally formed at the uppermost portion of fuel tanks in order to inhibit liquid fuels from flowing into the evaporator circuit. However, when the level of liquid fuels move up and down, there might arise a fear that liquid fuels flow into the evaporator circuit through the evaporator opening. If liquid fuels flow even into the canister, they adsorb onto the activated carbon so that they might impair the usual vaporized fuel-adsorbing action of the activated carbon.
Hence, the evaporator opening has been conventionally provided with a variety of cut-off valves. As for the cut-off valves, floating valves have been often used as described later. When the level of liquid fuels rises abnormally, the floating valves float upward by buoyancy to close the evaporator opening. Consequently, the floating valves inhibit liquid fuels from flowing into the evaporator circuit.
Moreover, fuel tanks are provided with means for detecting whether fuel tanks are filled up with fuels when fuels are supplied. As for the means for detecting filled-up fuel tanks, apparatuses comprising a floating valve have been often used as described later. The floating valve closes an opening of fuel tanks to heighten the pressure within fuel tanks. Thus, fuel supply guns are turned off automatically.
For example, Japanese Unexamined Patent Publication (KOKAI) No. 11-229,984 discloses an apparatus for inhibiting fuels from flowing out. The flow-out fuel inhibitor apparatus is provided with a shut-off valve and a cut-off valve. The shut-off valve lets a gas, which includes a fuel vapor generating in a large volume, flow to a canister when a fuel is supplied. The cut-off valve lets a gas, which includes a fuel vapor, flow to a canister when a fuel is not supplied. The flow-out fuel inhibitor apparatus produces an advantage that the number of component parts and the number of sealed portions can be reduced, because the shut-off valve, operating when a fuel is supplied, and the cut-off valve, operating when a fuel is not supplied, are accommodated in a housing.
However, the above-described flow-out fuel inhibitor apparatus requires two floating valves and two communication passages, respectively, which are disposed parallelly. Accordingly, there arises a problem that it is difficult to design so as to make each of them operate accurately. Moreover, the flow-out fuel inhibitor apparatus suffers from a drawback that the cost involved has gone up, because it requires two floating valves to result in increasing the number of component parts. In addition, the flow-out fuel inhibitor apparatus has a problem with a considerably limited disposition space, because it has an enlarged overall diameter.
Still further, when the above-described flow-out fuel inhibitor apparatus is applied to a variety of fuel tanks whose shape and capacity differ with each other, it is needed to manufacture a diversity of the flow-out fuel inhibitor apparatuses by varying the shapes of housing and float variously. Thus, there arises a drawback that the man-hour requirement for the manufacture has gone up enormously.
Hence, Japanese Unexamined Patent Publication (KOKAI) No. 8-105,571 discloses another apparatus for inhibiting fuels from flowing out. As illustrated in FIG. 6, the flow-out fuel inhibitor apparatus comprises a casing 100, a floating valve 200, a hole 101 with a larger opening area, and a hole 102 with a smaller opening area. The floating valve 200 is disposed in the casing 100. The hole 101 is formed in the bottom of the casing 100. The hole 102 is formed in the top of the casing 100.
The flow-out fuel inhibitor apparatus operates as hereinafter described. When a fuel is supplied, air within a fuel tank 300 is emitted in the following manner as the level of the liquid fuel rises. The air passes through the hole 101 having a larger opening area and hole 102 having a smaller opening area of the casing 100. Then, the air is emitted into a liquid reservoir 105 through an opening 104 by way of a gap 103, into an opened differential-pressure valve 106, into a gap 107, and into a pipe 108 which is connected to a canister and the like. Thereafter, when the hole 101 with a larger opening area is placed below the level of the liquid fuel, the air within the fuel tank 300 is emitted by way of the hole 102 with a smaller opening area alone. However, when the air is emitted through the hole 102 having a smaller opening area only, the air emission is decreased so less that the pressure increases within the fuel tank 300 to actuate a mechanism for turning off a fuel supply gun.
Subsequently, it is possible adjust the level of the liquid fuel to a filled-up liquid-level height “L2” by supplying the fuel with a slow rate which is reduced in accordance with the volume of the air emitted through the hole 102 having a smaller opening area. Moreover, when the level of the liquid fuel exceeds the filled-up liquid-level height “L2,” it is possible to inhibit the fuel from entering the pipe 108 which is communicated with the opening 104, because the opening 104, through which the air within the fuel tank 300 is emitted when the fuel is supplied, is closed by the floating valve 200.
However, in the flow-out fuel inhibitor apparatus disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 8-105,571, when the liquid level of the fuel moves up and down violently, there arises a drawback that the floating valve 200 does not respond to it satisfactorily. Specifically, the floating valve 200 is poor in term of the response to the up-and-down motions of the level of liquid fuels, because the mass of the floating valve 200 is large comparatively. Accordingly, there arises a drawback that liquid fuels enter the pipe 108 through the opening 104 to eventually flow to the canister. Moreover, if the floating valve 200 adheres to the opening 104, the floating valve 200 might not move downward even when the level of liquid fuels descends.
Hence, Japanese Unexamined Patent Publication (KOKAI) No. 2-112,658 discloses still another apparatus for inhibiting fuels from flowing out. The apparatus is provided with a double-floating valve. The double-floating valve comprises a lower float, and an upper float. The upper float is held to the top of the lower float so as to be movable up and down relatively, has a minor-diameter valve hole which is opened or closed by the lower float, and closes the evaporator opening. In accordance with the double-floating valve, even when the lower float descends, the upper float keeps to close the evaporator opening for a certain period of time because the upper float has a small mass. In this instance, the valve hole is opened. Thus, the gas within fuel tanks can flow toward the canister through the evaporator opening by way of the valve hole. Moreover, liquid fuels are inhibited from passing the valve hole, because the valve hole has a minor diameter. Accordingly, it is possible to inhibit liquid fuels from entering the canister. Therefore, the response to the up-and-down movements of the level of liquid fuels is improved. In addition, when the lower float moves further downward, accompanied therewith, the upper float moves downward to open the evaporator opening. Consequently, it is possible to inhibit such a drawback that the evaporator opening is kept being closed by the upper float even when the level of liquid fuels descends.
However, even in the flow-out fuel inhibitor apparatus provided with the double-floating valve, liquid fuels might enter the evaporator opening through the valve hole when the level of liquid fuels moves up and down violently. Specifically, liquid fuels might enter the evaporator opening through the valve hole in such a short period of time that the upper float closes the evaporator opening and the lower float moves downward to open the valve hole. If such is the case, a large pressure acts on liquid fuels because the valve hole has a minor diameter. As a result, liquid fuels might spout with great force through the valve hole.